The invention relates to dual cure resin compositions and, more particularly, such resin compositions with utility as primers for coil coatings.
Primers for coil coating must have a number of properties including corrosion protection for the metal substrate, flexibility so that the finished product can be rolled, good adhesion to both the metal substrate and the coating applied over the primer as well as application and cure properties so that the primer can be applied to a substrate and cured while the substrate is moving at a line speed of 300-400 feet per minute.
One conventional primer is an epoxy-urea formaldehyde based primer, which is typically applied and thermally cured to a 0.2-0.3 mils dry film thickness. A durable topcoat is then applied thereto and thermally cured. This type of conventional primer is limited to such a low dry film thickness because the composition is only approximately 60 percent, by weight, solids and, therefore, at the high line and curing speeds required for application, the coating blisters at high film builds due to solvent popping.
It is desired, therefore, to develop a composition that can be applied at higher film thicknesses than conventional primers in order to achieve better corrosion protection for the substrate.
Further, such conventional primer-topcoat systems require two baking steps, which involve a tremendous amount of energy. Thus, it is further desired to develop a coating system for protecting metal substrates that reduces the energy necessary to cure the coatings.